Systems and methods herein generally relate to printing systems, and more particularly to printing of clear and pigmented colorants on a media substrate in multi-pass operation of a printing apparatus.
In modern desktop printing systems, a document can be created or received in electronic form on a device such as a personal computer, a personal digital assistant, or other suitable device. Parameters of print jobs (such as for finishing, imposition, color management) can be set at the print queue, print job, page description language (PDL) creation, exception page creation, line printer remote (LPR), and job ticket level. Imposition settings are job settings that cause page images to be placed on print media at specific locations, orientations, and scalings. For example, a user can format the document, adjust the layout of the document, change fonts, change font sizes, etc. These settings are reconciled before a job is submitted for print. Thereafter, the document can be printed on a printer to produce a hardcopy of the document. The hardcopy of the document can further be bound or otherwise subjected to processing to result in a finished product.
Imposition is one of the fundamental steps in the prepress printing process. It consists in the arrangement of the printed product's pages on the printer's sheet, in order to print faster, simplify binding, and reduce paper waste. In particular, it allows the printer to set up such documents as business cards, magazines, flyers, postcards, and brochures. Print operators will print books using large sheets of paper that will be folded and trimmed later. This allows for faster printing, simplified binding, and lower production costs. Imposition is the process of arranging the pages correctly prior to printing so that they fold in the correct order. To someone unfamiliar with the imposition process, the pages may seem to be arranged randomly; but after printing, the paper is folded, bound, and trimmed. If correctly imposed, the pages all appear in the correct orientation and readable sequence.
Various printing systems support the loading of spot colorants in an extension print housing. The initial print housing generally supports the base colorants (e.g., C, M, Y, K (Cyan, Magenta, Yellow, and Black)). Many printing devices can produce printed output with the spot colorant in addition to CMYK. An additional colorant may include white or clear colorant.
A use of clear colorant on printed media sheets is becoming more diverse with newly discovered applications for using the clear colorant as a way to achieve particular visible effects. Typically, the printing device can support several options for the printing of clear and the CMYK colorants for multi-pass operations. For example, clear can be printed:
1. As the first pass(es) with a final pass adding the CMYK colorant. (aka Base clear)
2. As the 2nd (and later passes) with the CMYK colorants printed first                a. Over the entire page (aka flood clear)        b. Selectively on top of specified Objects (aka Object clear)        c. Via Page Description language constructs (aka Embedded clear)        d. Where no CMYK content appears (aka Infill clear)Additionally, the number of passes to be printed may be specified in combination with any of the above options. Each pass may be used to render one coat of the clear colorant layer.        
The current procedure for handling multiple pass clear is to RIP the page once. The CMYK and clear are applied on the first pass. Then, clear colorant only is applied on subsequent passes. However, an imposed printed sheet may have print ordering schemes for both CMYK and clear applied to the pages of a single sheet; and it may have varying numbers of passes specified for the pages. Current image processing capabilities do not support separate commands for each page of multiple pages on a single sheet of media. That is, a single set of image planes (e.g., cyan, magenta, yellow, black, or clear only) for the entire sheet is sent to the marking engine for a particular print pass. Hence, if one portion of the sheet requires clear on top of CMYK and another portion requires clear under CMYK this could not be accomplished.